RFID Tag Technology
Radio Frequency Identification (RFID) is an identification technology which relies on storing and retrieving data using devices called RFID tags. An RFID tag is in general a small object capable of functioning as a label, that can be attached to or incorporated into an item such as a commercial product, an animal, or a person.
Typically, an RFID tag consists of a small integrated circuit with a small storage capability and a radio antenna. Some tags, referred to as “active tags”, have an internal power source which is generally used to power any processing circuitry and to generate outgoing signals. Other tags, referred to as “passive tags” do not have any internal power source. Passive tags generally obtain the energy required for responding to incoming signals and generating outgoing signals by collecting energy from an electromagnetic field generated by a reader. Also, there exist tags known as “semi-active” (or sometimes “semi-passive”) tags, which generally have a small power source in order to enable the tag's processing circuitry to be powered constantly. These tags therefore do not need to collect energy from incoming signals before commencing any processing, allowing them generally to provide faster responses than passive tags, but active and semi-active lags are generally more expensive than passive tags.
An RFID tag generally holds identity information at least relating to an item with which it is associated. Current RFID tags typically offer a 96-bit identifier number that can be globally unique and addressable. Upon being queried by a reader, a tag generally responds with identity information which may point to a unique location in a database in which detailed information about the item may be stored. This may include product characteristics, data about the origin of the items the identity of a manufacturer and other manufacturing details, pricing information, any appropriate expiry dates, etc.
RFID technology is thought to be a possible at least partial replacement for barcode technology, for which there exists a standard called the Universal Product Code (UPC). An RFID tag can provide an identification number, as can a barcode, but unlike barcodes, RFID tags can be read at a distance without a line-of-sight requirement, and without human intervention. Due to this and due to their small size, RFID tags can be placed in boxes with, or even inside consumer items, can be attached to clothes, and can be used in a wide variety of other applications.
RFID tag technologies have been in use for many years but major technology development has happened in the last few years in particular through the Auto-ID Center in collaboration with the Massachusetts Institute of Technology (MIT). An aim was to make RFID tags as simple as possible, with very small chips and a cost per tag of less than 0.1 US$. At this level, it is thought that RFID tags will realistically start to replace the barcodes presently used in relation to many consumer products, and economies of scale will then enable research into new applications. It is likely that the first tags of a sufficiently small size and having a low-enough cost for the above will be passive tags.
Monitoring of Goods Being Moved
When items or goods are moved along supply chains their current location can be determined and recorded on a management system by a number of means. Typically, this is performed using barcodes associated with the items, or groups of items, that are scanned or read at strategic points along a supply chain path. There is an increasing trend to use RFID as this offers significant technical advantages over barcodes.
Monitoring the movement of goods along a supply chain is carried out for various reasons, for example, to prove that correct items have been detected at specific locations and also to gather data relating to the overall flow of goods within supply chains. The data recorded can serve a number of purposes 1) provide proof of dispatch or arrival, 2) enable queries to be resolved regarding, for example, the predicted arrival time of goods based on a statistical history 3) used to examine a supply chain so that any inefficiencies can be determined and removed 4) detect anomalies in the supply chain such as diversion of goods.
To obtain an accurate indication of the movement of goods within supply chains it is necessary to have significant number of RFID read-points (an RFID read-point is generally an RFID reader and an aerial array at a known physical location and with a network connection for transferring data). In many applications, there are only a minimum number of read-points that are available and no information about the movement of goods between the read-points is possible.
Being able to know the movement profile of goods in transit between read-points can aid in detecting departures from the norm and help in improving efficiency of the supply chain by identifying periods of time when items are static and not being moved.
Generally, passive RFID tags or barcodes alone are not able to register the fact that an item has been disturbed or displaced.
An RFID tag can be purely passive (without its own power source) and is primarily capable of relaying a unique identity. Other variants of passive RFID tags (such as semi-passive RFID tags) are capable of storing data. Alternatively, RFID tags can have an associated power source such as an on-board battery either to extend the reading-distance range or to add extra sensing and/or processing functionality. As well as increased cost and size, however, a disadvantage of active RFID tags is the finite battery-life of the associated power supply.
Radio-location
Location using multiple RF sources each having a known location. This can be achieved by using Wi-Fi access points, cellular radio base stations and rely on powered receivers to calculate relative position using triangulation, time of arrival, etc. Variants of these systems can work indoors and outdoors with limited accuracy.
GPS functions in a similar manner where the orbit of satellites is predetermined. Generally GPS is a system that will only reliably work outdoors with powered receivers.
Energy Scavenging
There are many techniques for scavenging energy: optical, acoustic and temperature differential, etc. Of particular interest are those systems that harvest RF energy (e.g. from RFID readers) and those that convert motion or mechanical vibration to electrical energy.
A UK-based company called “Perpetuum” produces batteryless devices such as a vibration energy harvester known as the “PMG17” micro-generator, further information about which can be found on the internet at http://www.perpetuum.co.uk/home.php?page id=11. Such devices are capable of converting vibration into electrical energy.
Perpetual mechanisms can be constructed using an oscillating fan-shaped rotor weight that swings on a pivot. The weight that rotates in both directions can be used in wristwatches to wind the mainspring as the watch is being worn. An extension of this mechanism would be to convert the stored mechanical energy into electrical energy.
Tracking Devices
The Letter Logger: http://www.trackingtheworld.com/letterlogger.htm is a battery-powered letter tracking device which receives GPS signals and stores the location data. Operation can be triggered in a tilt mode which reports only when a tilting movement is detected.